1. Field of the Invention
This invention pertains to the field of structural bearings used to support bridges and buildings. More particularly, this invention pertains to improvements in structural bearings that render them capable of lower manufacturing and installation costs than those presently on the market, as well as enhanced qualities such as the ability to withstand greater and more varied loads.
2. Description of the Prior Art
It has been known, for many years, to place bearings under large buildings and bridges where they contact the earth. The dead weight of the structure must be supported. In addition, thermal expansion of the structure, wind striking the sides of the structure, and earthquake temblors all place loads on the structure that will move the structure and cause damage to the underlying support piers and pilings unless a means is provided for relieving the stresses generated by these loads.
Most structural bearings include a layer or layers of elastomeric material such as natural rubber, polyurethane rubber, EPDM (ethylene propylene diamine) rubber, SBR (styrene butadiene rubber), Neoprene.RTM. rubber and the like. The rubber layer takes the vertical load in compression from the dead weight of the building while most of the other loads (wind and earthquake) create horizontal forces that place the rubber layer in shear. Other loads, such as rotation, turning, and tilting are created by a combination of these forces. All of them must be adequately contained in the structural bearing in order to prolong the quality of the building or bridge construction.
The prior art structural bearings have in large part been created by me and are disclosed and claimed in my previous patents, such as U.S. Pat. Nos. 3,806,975; 3,921,240; and, 4,187,573. These bearings are rather expensive to manufacture and require certain skills in setting and installing them. Many of them cannot be visually inspected because of where they must be installed.
Structural engineers are designing buildings and bridges that place increased demands on these bearings. These demands require that the bearings support a greater dead load and be capable of handling a variety of transient loads, as well as be cheaper to construct and easier to install in locations capable of visual inspection after installation. Further, they must be handled by persons of lesser abilities than before due to the general decline in competency in the American work force.